I am looking into whether it would be a good idea(not a terrible idea) to remove the brownout circuit from the xCore-200 MC audio board. I did not find any info on it in the XMOS documents. I am looking to make a new circuit as cheap as possible so I am not interested in stuff that are " good to have" just the "musts". Does anyone have an opinion on this? How exactly is this brownout circuit working?

I'd advise you to follow the reference schematics and schematic design checklist for the xCORE-200 microcontroller, e.g. Chapter 5 and Appendix H of XEF216-512-TQ128 Datasheet. You will need a reset supervisor of some description but it doesn't have to be precisely identical to the MC audio board's schematic. 1. You will need to follow H.1 in Appendix H. The XMOS circuit is specifically design to ensure that the 1.0V core supply follows those requirements (namely, that the IO voltage is 3.3V before turning on the core, and the core voltage rises to 1.0V within 10ms).2. If you have an open drain output for POR_N then you can directly connect POR_N and XSYS_RST_N, so you can avoid U26; that works fine for me.

One option that will probably work is to use an IO regulator with a power good (PG) output, and use the PG output to enable the 1.0V supply. But provide DNP footprints for more sophisticated circuitry in case the simplest solution doesn't work over your full operating temperature range.